1. Field of the Invention
The present invention relates generally to manhole covers. More particularly, the present invention relates to a resilient pad that is attachable to a manhole cover.
2. Related Art
Manholes are common structures in streets and roadways for allowing access to underground utilities such as water and sewer lines or stored materials or equipment. Manholes provide an opening to allow workmen to descend beneath the surface to obtain access to these underground items. Manholes and manhole covers are typically subject to significant loads, such as the weight of roadway vehicles and impact loads from them, and thus must be made of strong and durable materials. The top of a manhole typically includes a strong metal (e.g. cast iron) frame having a projecting ledge around the circumference of the opening, with a heavy cast iron cover that rests on the ledge and closes the manhole. The cover is designed to support surface loads, and the frame transmits those loads to the underground supporting structure. Manhole covers are generally made heavy to resist unintentional opening or vandalism, and in many cases are bolted down in order to make the installation water tight and tamper-proof.
One challenge associated with manhole installations is maintaining the manhole cover flush with a surrounding roadway elevation. When a street is repaved, the pavement elevation increases by a few inches. Manholes can also settle over time, producing an elevation difference with surrounding pavement. If these conditions are not corrected, the manhole location can present a road hazard, the manhole cover and supporting structure will be subjected to increased impact loads from passing vehicles, and the surrounding pavement is likely to degrade more quickly. To avoid these problems, road paving crews sometimes simply pave over an existing manhole. Unfortunately, this defeats the whole purpose of the manhole, and hides its location from view.
More commonly, when a street is repaved or a manhole has settled, existing manholes in the street are typically raised to match the elevation of the pavement. This process typically involves the installation of new grade rings or other structures atop the manhole frame to raise its elevation, and may also involve the installation of a new concrete collar surrounding the manhole to reinforce the transition from asphalt pavement to the rigid cast iron manhole top. Unfortunately, raising manholes in a street can be an expensive and time-consuming process, thus adding to the financial burden that highway maintenance agencies face in building and maintaining roadways.